The near surface ultrafine grains (NSUFG) layer with grain sizes of about 35nm to 200nm from surface to about 10μm was prepared in the OFHC-Cu sheet with coarse grains size of about 7.2μ m (CG-Cu) by Near Surface Sever Plastic Deformation method. The solid reactions of Sn to NSUFG layer and CG-Cu were basically investigated at 379K to 493K for 1x103 to 6x106s. The Cu6Sn5 (η) and Cu3Sn (ε) layers were formed between Cu and Sn. The thickness of the ε layer in NSUFG-Cu/Sn was similar to that in CG-Cu/Sn one, while the thickness of the η layer in NSUFG-Cu/Sn reaction was about two times thicker than that in CG-Cu/Sn one. This enhancement of the η layer growth in NSUFG-Cu/Sn reaction was due to the large supply of Cu atoms to the reaction layer by the grain boundary diffusion in the NSUFG-Cu. The rate-controlling processes of layer growth were boundary diffusion mechanism in reaction layer at lower temperatures in shorter annealing time, and volume diffusion mechanism at higher temperatures in longer annealing times.